Rotational Device with Eccentric Abrasive Element and Method of Use

ABSTRACT

A rotational device for removing an occlusion from inside a tubular structure, the device comprising a drive shaft ( 10 ) for insertion over a guidewire into a tubular structure and an abrasive element ( 20 ) on the drive shaft having its centre of mass offset from a longitudinal axis of the drive shaft. A solid counterweight ( 30 D) is disposed on the drive shaft spaced from the abrasive element and having its centre of mass offset from the longitudinal axis of the drive shaft so that the abrasive element moves in an orbital path around said axis to abrade an occlusion from inside the tubular structure when the drive shaft rotates around the guidewire.

The invention relates to devices for removing material from the interiorof tubular structures. More specifically, the invention relates to adevice for removing or reducing occlusions, and other unwanted depositsfrom the interior of blood vessels or other tubular structures byrotating an abrasive element (e.g., burr) within the structure topartially or completely eliminate the unwanted material.

Atherosclerosis, the clogging of arteries, is a leading cause ofcoronary heart disease. Blood flow through the peripheral arteries(e.g., carotid, femoral, renal, etc.), is similarly affected by thedevelopment of atherosclerotic blockages. One existing method ofremoving or reducing blockages in blood vessels is known as rotationalor ablative atherectomy. A long guidewire is inserted into the desiredblood vessel and across the stenotic lesion, and a hollow drive shaft isadvanced over the guidewire. The distal end of the drive shaftterminates in a burr provided with an abrasive surface such as diamondgrit or diamond particles. The burr is positioned against the occlusion,and the drive shaft is rotated at extremely high speeds (e.g.,20,000-160,000 rpm). The abrasive surface of the burr scrapes againstthe occluding tissue and disintegrates it, reducing the occlusion andimproving the blood flow through the vessel. Such a method and a devicefor performing the method are described in, for example, U.S. Pat. No.4,990,134 to Auth, and U.S. Pat. No. 6,132,444 to Shturman (the instantinventor) et al. In the Shturman device, the abrasive element is locatedproximally to and spaced away from the distal end of the drive shaft.

In some systems, including the one described in U.S. Pat. No. 6,132,444to Shturman et al, the abrasive element is formed as an eccentric masspositioned a short distance proximal from the distal end of the driveshaft. That is, the abrasive element may be circular, oval, or may haveanother shape in longitudinal cross section, however the center of mass(or center of gravity) of the abrasive element is not collinear with therotational (longitudinal) axis of the drive shaft. The intention is thatthe eccentric mass, when rotated rapidly, will attempt to move away fromthe rotational axis and actually orbit around the rotational axis,thereby creating a much larger opening than the diameter of the abrasiveelement itself. However, in practice, such a system has significantlimitations in opening stenotic lesions to a diameter substantiallylarger than that of the abrading element. Limitations in the swath of asingle eccentric abrasive element manifest because of a tendency of thesingle eccentric abrasive element to rotate around its own center ofmass which does not coincide with the guidewire around which the driveshaft is rotated. As a result, the rapidly rotating eccentric mass tendsto force both the drive shaft and the guidewire to orbit a point whichis relatively close to the center of mass of the eccentric element. Thelimited maximum swath of an orbital abrasive device with a singleeccentric element is explained by the single rapidly rotating eccentricmass pushing the guidewire in the direction 180° opposite the mosteffective area of the abrasive surface. Also, the entire assembly(abrasive element, drive shaft, and guidewire) has the tendency tovibrate during rotation in a less-than-perfectly-controlled fashion.

Accordingly, the present invention seeks to provide a rotational devicefor removing or reducing deposits from the interior of tubularstructures, preferably biological structures such as arteries, veins,arteriovenous grafts, shunts, and the like.

The invention also seeks to provide a method and device for orbitalangioplasty which reduces vibrations of the drive shaft.

It is known to provide a rotational device for removing an occlusionfrom inside a tubular structure, the device comprising a drive shaft forinsertion into a tubular structure and an abrasive element on the driveshaft having its centre of mass offset from a longitudinal axis of thedrive shaft.

A rotational device according to the present invention is characterisedby a solid counterweight on the drive shaft spaced from the abrasiveelement and having its centre of mass offset from the longitudinal axisof the drive shaft so that the abrasive element moves in an orbital patharound said axis to abrade an occlusion from inside the tubularstructure when the drive shaft rotates.

It is also known to provide a rotational device comprising a drive shafthaving a distal end section formed from at least one helically woundwire and an abrasive element on the distal end section having its centreof mass offset from a longitudinal axis of the drive shaft.

A rotational device according to the invention is also characterised bya solid counterweight on the distal end section spaced from the abrasiveelement and having its centre of mass offset from the longitudinal axisof the drive shaft.

In a preferred embodiment, the rotational device comprises two solidcounterweights on the drive shaft. Preferably the rotational deviceincludes a distal solid counterweight distal to the abrasive element onthe drive shaft and, a proximal solid counterweight proximal to theabrasive element on the drive shaft.

Advantageously, the distance between the distal solid counterweight andthe abrasive element and between the proximal solid counterweight andthe abrasive element is substantially the same.

Preferably, the distal solid counterweight is disposed on the distal endof the drive shaft.

In an advantageous embodiment of the invention, the centre of mass ofthe or each solid counterweight is located in substantially the samelongitudinal plane as the centre of mass of the abrasive element.Preferably, the centre of mass of the or each solid counterweight isdiametrically opposite to the centre of mass of the abrasive elementwith respect to the longitudinal axis of the drive shaft. Mostpreferably, the centre of mass of the or each solid counterweight isseparated from the centre of mass of the abrasive element by an angle of180 degrees around the axis of the drive shaft.

Conveniently, the or each solid counterweight includes a shoulder thatcooperates with a corresponding shoulder on the drive shaft to mount theor each solid counterweight to the drive shaft. Preferably, the shoulderon the drive shaft is formed from a layer of metal applied to the driveshaft.

The layer of metal applied to the drive shaft that cooperates with theor each solid counterweight may conform to the outer surface of thedrive shaft.

In another embodiment, an adhesive layer is disposed between the or eachsolid counterweight and the drive shaft.

Preferably, the or each solid counterweight is rounded.

Advantageously, the or each solid counterweight is substantiallyspherical in shape. Alternatively, a longitudinal cross section of theor each solid counterweight is substantially elliptical in shape.Similarly, a longitudinal cross-section of the abrasive element may besubstantially elliptical in shape.

solid counterweight In a preferred embodiment, the or each solidcounterweight is substantially half the weight of the abrasive element.

In the preferred embodiment, the or each solid counterweight iseccentrically disposed on the drive shaft.

The rotational device preferably includes a guidewire for insertion intoa tubular structure prior to insertion of the drive shaft, the driveshaft being configured for insertion into the tubular structure over theguidewire.

According to another aspect of the invention, there is provided anatherectomy device for the removal of an occlusion from the interiorwall of a blood vessel such as a coronary artery, bypass graft or otherbiological or non-biological tubular structure, comprising a rotationaldevice according to the invention.

According to another aspect of the invention, there is provided acatheter for the removal of an occlusion from the interior wall of abiological structure comprising a rotational device according to theinvention.

It is also known to provide a method of making a rotational device forremoving an occlusion from inside a tubular structure, comprising adrive shaft for insertion into a tubular structure and an abrasiveelement on the drive shaft having its centre of mass offset from alongitudinal axis of the drive shaft.

A method of making a rotational device according to the presentinvention is characterised by the step of attaching a solidcounterweight on the drive shaft spaced from the abrasive element andhaving its centre of mass offset from the longitudinal axis so that theabrasive element moves in an orbital path around said axis to remove anocclusion from the tubular structure when the drive shaft rotates.

In a preferred embodiment, the method includes the step of attaching twosolid counterweights to the drive shaft.

Preferably, the method includes the step of forming correspondingshoulders on the drive shaft and on the or each solid counterweight thatcooperate to mount the or each solid counterweight to the drive shaft.

Conveniently, the method of forming a shoulder on the drive shaftcomprises the step of applying a layer of metal to the drive shaft. Themethod may include the step of gluing the solid counterweights to thedrive shaft using adhesive. Alternatively, the method includes the stepof soldering, welding or press-fitting the or each solid counterweightto the drive shaft.

The present invention also provides a method of using a rotationaldevice to remove an occlusion from inside a tubular structure,comprising the steps of inserting a drive shaft with an abrasive elementthereon into a tubular structure, the abrasive element having its centreof mass offset from a longitudinal axis of the drive shaft and, rotatingthe drive shaft so that a solid counterweight on the drive shaft havingits centre of mass offset from the longitudinal axis of the drive shaftcauses the abrasive element to move in an orbital path around said axisto abrade an occlusion from inside the tubular structure.

The rotational device preferably includes a guidewire and the methodpreferably includes the step of partially withdrawing the guidewire intothe lumen of the drive shaft such that the distal end of the guidewireis located within the lumen of the drive shaft proximal to the distalend section of the drive shaft thereby making the distal end section ofthe drive shaft more flexible.

It is intended that, when the drive shaft of the rotational deviceaccording to the invention is rotated, centrifugal forces generated bythe solid counterweights and the abrasive element preferably act insubstantially the same plane but in opposite directions. Thesecentrifugal forces cause the distal section of the drive shaft to flexand generally assume a bowed shape. As a result, the abrasive element,as well as both solid counterweights, move in orbital fashion around theaxis of rotation of the drive shaft in orbits that are substantiallylarger than the respective diameters of the abrasive element or solidcounterweights.

Pressure applied by the abrasive element and the solid counterweights tothe tissue to be removed or to the inner surface of the vessel wall caneasily be controlled by controlling the rotational speed of the driveshaft (i.e., the faster the speed of rotation, the greater the appliedpressure), as well as by selecting the respective weights of theabrasive element and solid counterweights. Applied pressure is alsoaffected by the distances between the abrasive element and the solidcounterweights, since the distances affect the momentums which cause thedrive shaft to bow.

As a result, the overall radial profile of the distal end section of thedrive shaft in use is much larger than its motionless profile. Theinventive device therefore can be used to abrade deposits formed on theentire inner surface of the wall or at least a greater portion of theinner surface of the wall of a tubular biological structure such as ablood vessel very efficiently. Yet despite the increased efficiency ofthe device, it may be easily inserted via a small arterial puncture oropening, because when the drive shaft is not rotated about itslongitudinal axis, the distal end section of the drive shaft issubstantially only as wide as the maximum width of its abrasive elementor solid counterweights. Further, the provision of solid counterweightsgreatly reduces or eliminates unwanted vibration in the drive shaftduring rotation.

It should be noted that the eccentric disposition of the abrasiveelement and solid counterweights is not limited to their geometricaleccentric position but, much more importantly, involves the eccentricdisposition of their centers of mass with respect to the rotational axisof the drive shaft.

Embodiments of the invention will now be described, by way of exampleonly, with reference to the accompanying drawings, in which:

FIG. 1 is a perspective view of an orbital/rotational atherectomy deviceincorporating the invention.

FIG. 2 is an enlarged view of the distal end section of theorbital/rotational atherectomy device incorporating the invention ofFIG. 1.

FIG. 3A is a side sectional view of the distal end section of theorbital/rotational atherectomy device incorporating the invention takenalong line 3-3 of FIG. 2.

FIG. 3B is a schematic of the proximal side of FIG. 3A illustrating thecenters of mass and resultant forces which occur when the device isrotated.

FIG. 3C is a schematic of the distal side of FIG. 3A illustrating thecenters of mass and resultant forces which occur when the device isrotated.

FIG. 3D is a schematic of FIG. 3A illustrating the centers of mass andresultant forces which occur when the device is rotated and effect ofthese forces on the shape of the distal end section of the drive shaft.

FIGS. 4-7 are successive sectional views of the rotating deviceaccording to the invention of FIG. 2 being moved over a guidewire andablating deposits in a blood vessel.

FIGS. 8-11 are successive sectional views of the rotating deviceaccording to the invention of FIG. 2 ablating deposits in a blood vesselwhen drive shaft is rotated around the guidewire which has beenwithdrawn into the lumen of the drive shaft such that the distal end ofthe guidewire is located within the lumen of the drive shaft proximal tothe distal end portion of the drive shaft.

FIG. 12 is a sectional view of an alternate embodiment of the inventionhaving a single distal solid counterweight.

FIGS. 13-16 are successive sectional views of the device according tothe invention of FIG. 12 when the drive shaft has been advanced over aguidewire and ablating deposits in a blood vessel.

FIGS. 17-20 are successive sectional views of the device according tothe invention of FIG. 12 ablating deposits in a blood vessel when thedrive shaft is rotated around the guidewire which has been withdrawninto the lumen of the drive shaft such that the distal end of theguidewire is located within the lumen of the drive shaft proximal to thedistal end portion of the drive shaft.

FIG. 21 is a side sectional view of an embodiment of the inventionshowing structure attaching the distal solid counterweight to the driveshaft.

FIG. 22 is an enlarged side sectional view of the structure attachingthe distal solid counterweight to the drive shaft of FIG. 21.

FIG. 23 is a side sectional view of another embodiment of the inventionshowing structure attaching the distal solid counterweight to the driveshaft.

FIG. 24 is an enlarged side sectional view of the structure attachingthe distal solid counterweight to the drive shaft of FIG. 23.

FIG. 25A is a sectional view of another embodiment of the inventionwhere the central eccentric abrasive element is formed from windings ofthe drive shaft.

FIG. 25B is a sectional view of another embodiment of the inventionhaving a single solid counterweight and where the central eccentricelement is formed from windings of the drive shaft.

FIGS. 26 to 29 depict varying geometries of the eccentric abrasiveelement and solid counterweights for a device in accordance with theinvention.

FIG. 1 is a perspective view of a rotational atherectomy device inaccordance with an embodiment of the invention. The advancer 3 issimilar to that described in the Shturman patent mentioned above. Itshould be understood that any type of advancer may be used, includingbut not limited to advancers described by Auth, other advancersdescribed by Shturman, and advancers developed by others. The instantimprovements appear in the distal end section of the drive shaft and areoutlined by the dashed line box of FIG. 1 and best illustrated in FIG.2.

Drive shaft 10 is provided with an eccentric abrasive element or burr 20on its distal end section at a predetermined distance from the terminusof the drive shaft. At or near the terminus of drive shaft 10 isdisposed an eccentric solid counterweight 30D. Preferably, a secondeccentric solid counterweight 30P is disposed on drive shaft 10 proximalto abrasive element 20. It is more preferable that the distance betweensolid counterweight 30P and abrasive element 20 is substantially equalto the distance between abrasive element 20 and solid counterweight 30D.As shown in FIG. 3A, abrasive element 20 is secured to drive shaft 10via adhesive layer 26, and solid counterweights 30P and D are secured todrive shaft 10 via adhesive layers 36P and 36D, respectively. Abrasiveelement 20 has an abrasive surface 22, which may be formed by depositionof an abrasive material (e.g., diamond grit), or similar abrasiveproperties may be provided to the surface using laser, electricaldischarge machining (EDM), or other methods of micro- or nano-machining.

FIGS. 3A-D illustrate the inventive mass distribution of the instantdevice. None of eccentric abrasive element 20 or solid counterweights30P or 30D is disposed on drive shaft 10 with its center of masscollinear with the drive shaft. As best shown in FIG. 3A, abrasiveelement 20 has a center of mass 24 which, in this configuration, isabove drive shaft 10. Both solid counterweights have respective centersof mass 34P and 34D which, in this configuration, are below drive shaft10. The references to “above” or “below” the drive shaft refer only tothe illustration; the drive shaft is basically radially symmetrical and,conceptually, it is sufficient for the center of mass 24 to be “above”and the centers of mass of the solid counterweights 30 to be “below” therotational axis of the drive shaft. That is, the centers of mass 34 ofthe solid counterweights 30 are preferably diametrically opposite thatof abrasive element 20 (e.g., 180° around from the center of mass of theabrasive element 20 or thereabouts).

The significance of this weight distribution can best be explained withreference to FIGS. 3B-D. In FIG. 3B, the proximal portion of the distalend section of drive shaft 10 is shown. Point A is a central point (orcenter of mass) between solid counterweight 30P and abrasive element 20.Because center of mass 34P is on one side of drive shaft 10 and centerof mass 24P (the center of mass of the proximal half of the abrasiveelement 20) is on the other side, rotation of drive shaft 10 in thedirection of arrow C causes solid counterweight 30P to be pulled in thedirection of arrow F_(3P) and abrasive element 20 to be pulled in thedirection of arrow F_(2P). Both arrows F_(3P) and F_(2P) representcentrifugal forces acting in the same rotating longitudinal plane but insubstantially opposite directions with respect to the rotational axis ofthe drive shaft. Accordingly, the section of drive shaft 10 shown inFIG. 3B tends to rotate about point A as shown by the dashed line 10′.

Similarly, in FIG. 3C, the distal portion of the distal end section ofdrive shaft 10 is shown. Point B is a central point between solidcounterweight 30D and abrasive element 20. Because center of mass 34D ison one side of drive shaft 10 and center of mass 24D (the center of massof the distal half of abrasive element 20) is on the other side,rotation of drive shaft 10 in the direction of arrow C causes solidcounterweight 30D to be pulled in the direction of arrow F_(3D) andabrasive element 20 to be pulled in the direction of arrow F_(2D) asbefore. Accordingly, the section of drive shaft 10 shown in FIG. 3Ctends to rotate about point B in the direction shown by the dashed line10″.

The combination of the two force diagrams FIGS. 3B and C is shown inFIG. 3D. Preferably, the centers of mass 34P and D of the solidcounterweights 30P and D are disposed in the same radial position aboutdrive shaft 10, and preferably that position is 180° around from theradial position of center of mass 24. When drive shaft 10 is rotatedabout its longitudinal axis, all three bodies disposed on drive shaft 10cause the distal end section of drive shaft 10 to bow or flex withmaximum deflection substantially at abrasive element 20 as shown by thedashed line 10′″ and dashed outline of abrasive element 20′. (For thepurpose of simplicity in FIG. 3D, only eccentric abrasive element 20shown to be moving, rather than the abrasive element and the solidcounterweights 30 moving in opposite directions.). As a result, insteadof the path of the rotating abrasive surface 22 being limited to themaximum diameter of abrasive element 20, the path of abrasive surface 22is greatly expanded and moves in orbital fashion within vessel 100.

The advantages of this expansion of the “reach” of the abrasive surfaceare readily understandable in view of FIGS. 4-7, which depict theinvention being used to reduce a partial occlusion 105 of a blood vessel100. In all of FIGS. 4-7, drive shaft 10 is being rotated within sheath35 in the direction of arrow C and being advanced longitudinally withinvessel 100 over guidewire 5 in the direction of arrow D. As drive shaft10 is rotated, abrasive element 20 bows outward from the axis ofrotation toward the wall of vessel 100, thereby increasing the overallswath that may be abraded by the device. In the first half of a rotation(FIG. 4), abrasive element 20 abrades against a lower portion ofocclusion 105 in vessel 100. In the second half of a rotation (FIG. 5),abrasive element 20 abrades against an upper portion of occlusion 105 invessel 100. In this way, the device can abrade the entire interiorcircumferential surface of the vessel 100, removing a thin layer oftissue as it is moved along the occlusion. Multiple forward and backwardpasses may be needed to reduce or remove the occlusion safely. Abradedparticles (AP) in this embodiment of the invention travel distally alongthe treated vessel together with flow of flushing fluid, blood orradiopaque solution. Abraded particles may vary in size depending onsize of particles forming abrasive surface of the abrasive element,rotational speed of such abrasive element and, most importantly, thedegree of uniformity of the stenotic tissue which is being removed. Theless uniform is the stenotic tissue, the higher the probability thatlarger size particles may be produced by the rotating abrasive elementand travel distally along the treated vessel. For example, irregularlycalcified stenotic tissue is expected to produce abraded particles (AP)of larger size. Radiopaque solution may be injected into the treatedvessel after each pass or several passes in order to appreciate progressof tissue removal and assure safety of the procedure. The position ofthe distal end of the sheath 35 may be better visualized by placingradiopaque marker 40 at the distal end of the sheath 35.

FIGS. 8-11 depict essentially the same process as FIGS. 4-7 but in whichthe guidewire 5 has been withdrawn into the lumen of the drive shaftsuch that the distal end of the guidewire is located within the lumen ofthe drive shaft proximal to the end section of the drive shaft, therebymaking the distal end section of the drive shaft more flexible.

FIG. 12 depicts an alternate embodiment of the invention. Drive shaft110 is provided with an abrasive element 120 having abrasive surface 122and an eccentric center of mass 124 as before. However, instead of twosolid counterweights, a single solid counterweight 130 having eccentriccenter of mass 134 is provided, preferably at the distal tip of driveshaft 110. As shown in FIGS. 13-20, drive shaft 110 will bow moregradually on the proximal side of abrasive element 120 than in theembodiment of FIGS. 4-12. FIGS. 13-16 depict the second embodiment beingused in an occluded blood vessel 100 over the guidewire 5, and FIGS.17-20 depict the second embodiment in which the guidewire 5 has beenwithdrawn into the lumen of the drive shaft such that the distal end ofthe guidewire is located within the lumen of the drive shaft proximal tothe end section of the drive shaft, thereby making the distal endsection of the drive shaft more flexible.

FIGS. 21-24 illustrate two variations in the means by which distal solidcounterweight 30D is secured to drive shaft 10 (FIGS. 21 and 23 are thefull views, while FIGS. 22 and 24 are enlarged views). The solidcounterweight is preferably provided with a shoulder or stepped portion38 in its internal bore 37 to become secured with adhesive 36 or othermedium onto a projection or flange formed on the drive shaft 10. It willbe appreciated that the solid counterweight(s) and/or the abrasiveelement may alternatively be attached to the drive shaft 10 by, forexample, soldering or welding. The variation of FIGS. 21 and 22 includesa thin coating or layer of metal 14 formed over the wrapped wires of thedrive shaft 10 which conforms in profile to the coils of drive shaftwire; consequently, layer 14 is ridged. The layer 14A of FIGS. 23 and 24is thicker and is flat and smooth on its outer surface. In eitherconfiguration, and in others not shown, solid counterweight 30D willremain securely on the distal end of drive shaft 10.

The geometries of the abrasive element and solid counterweightsdescribed above are substantially spherical. However, otherconfigurations are also contemplated. For example, FIGS. 25A-B depict adrive shaft 210 having an abrasive element 220 which is formed fromwindings of the drive shaft. Abrasive element 220 is provided withabrasive surface 222 and an eccentric center of mass 224 as before.Solid counterweights 230P and D are substantially similar to solidcounterweights 30P and D described above. FIG. 25B illustrates a singlesolid counterweight 230 associated with the abrasive element 220 of theembodiment shown in FIG. 25A. FIGS. 26 to 29 depict other shapes thatmay be employed for the abrasive element 20 and/or solid counterweights30D and 30P. Any convenient shape may be employed.

The invention is not limited to the above description. For example, theabrasive element and solid counterweights are shown to be adhesivelysecured to the drive shaft. However, the solid counterweights andabrasive element may be secured to the drive shaft be any known means,including soldering, welding, press-fitting, and the like.Alternatively, the solid counterweights may be made of silicone andsimply formed around the drive shaft. Similarly, these structures asshown are sectioned as solid metal with the heavier side (the one withthe center of mass) being larger than the other side. However, there aremany ways to accomplish the eccentricity of the center of mass. Some ofthe ways to achieve this that are contemplated as being within the scopeof the invention are as follows: use two or more different materials,one heavier than the other (e.g., gold and aluminum); make one sectionof the solid counterweight or abrasive element hollow and the othersolid; make one section hollow but fill it at least partially with aheavy material; and the like.

Also, the invention is described chiefly in context of angioplasty(primary atherectomy or restenosis), however the invention is alsoadaptable for use to clear any arterial or other vascular structures.Moreover, the invention is also highly suited to clear arterial orarteriovenous shunts, particularly those used for renal dialysis. Theinvention is not limited to biological systems either. The device may bescaled up to a more macroscopic size (e.g., inches instead ofmillimeters), if needed, and has utility in cleaning the insides ofpipes and tubing in the chemical, aerospace, plumbing, and HVAC fields,for example.

The use of solid counterweights in the form of separate elements whichare attached to the drive shaft is preferred. However, the drive shaftitself may be made with a localized eccentric weight distribution, e.g.,through the eccentric wrapping of several coils of wire, to form bulgesin the drive shaft that serve to counterbalance the eccentric abrasiveelement taught above.

1-15. (canceled)
 16. A rotational device, comprising: a drive shafthaving a distal end section formed from at least one helically woundwire and an abrasive element on the distal end section having its centreof mass offset from a longitudinal axis of the drive shaft, and a solidcounterweight on the distal end section spaced from the abrasive elementand having its centre of mass offset from the longitudinal axis of thedrive shaft.
 17. A rotational device according to claim 16, comprisingtwo solid counterweights on the drive shaft.
 18. A rotational deviceaccording to claim 17, comprising a distal solid counterweight distal tothe abrasive element on the drive shaft and, a proximal solidcounterweight proximal to the abrasive element on the drive shaft.
 19. Arotational device according to claim 18, wherein the distance betweenthe distal solid counterweight and the abrasive element and between theproximal solid counterweight and the abrasive element is substantiallythe same.
 20. A rotational device according to claim 18, wherein thedistal solid counterweight is disposed on the distal end of the driveshaft.
 21. A rotational device according to claim 18, wherein the centreof mass of at least one of the solid counterweights is located insubstantially the same longitudinal plane as the center of mass of theabrasive element.
 22. A rotational device according to claim 18, whereinthe centre of mass of at least one of the solid counterweights isseparated from the center of mass of the abrasive element by an angle of180 degrees around the axis of the drive shaft.
 23. A rotational deviceaccording to claim 18, wherein at least one of the solid counterweightsis substantially spherical in shape.
 24. A rotational device accordingto claim 17, wherein at least one of the solid counterweights issubstantially half the weight of the abrasive element.
 25. A method ofusing a rotational device to remove an occlusion from inside a tubularstructure, comprising the steps of: inserting a drive shaft with anabrasive element thereon over a guidewire into a tubular structure, theabrasive element having its center of mass offset from a longitudinalaxis of the drive shaft; and rotating the drive shaft over the guidewireso that a solid counterweight on the drive shaft having its center ofmass offset from the longitudinal axis of the drive shaft causes theabrasive element to move in an orbital path around said axis to abradean occlusion from inside the tubular structure.